EP3251356B1 - Palette mode coding for video coding - Google Patents

Palette mode coding for video coding Download PDF

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Publication number
EP3251356B1
EP3251356B1 EP16704738.0A EP16704738A EP3251356B1 EP 3251356 B1 EP3251356 B1 EP 3251356B1 EP 16704738 A EP16704738 A EP 16704738A EP 3251356 B1 EP3251356 B1 EP 3251356B1
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Prior art keywords
palette
syntax element
block
video
coding
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German (de)
English (en)
French (fr)
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EP3251356A1 (en
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Wei PU
Marta Karczewicz
Rajan Laxman Joshi
Feng Zou
Vadim Seregin
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Qualcomm Inc
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Qualcomm Inc
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/186—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a colour or a chrominance component
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
    • H04N19/176—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/189—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding
    • H04N19/196—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/30—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using hierarchical techniques, e.g. scalability
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/44—Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/593—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving spatial prediction techniques
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/70—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by syntax aspects related to video coding, e.g. related to compression standards

Definitions

  • This disclosure relates to video encoding and decoding.
  • Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radio telephones, so-called "smart phones," video teleconferencing devices, video streaming devices, and the like.
  • Digital video devices implement video compression techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), the High Efficiency Video Coding (HEVC) standard presently under development, and extensions of such standards.
  • the video devices may transmit, receive, encode, decode, and/or store digital video information more efficiently by implementing such video compression techniques.
  • Video compression techniques perform spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences.
  • a video slice e.g., a video frame or a portion of a video frame
  • Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture.
  • Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures.
  • Pictures may be referred to as frames, and reference pictures may be referred to as reference frames.
  • Residual data represents pixel differences between the original block to be coded and the predictive block.
  • An inter-coded block is encoded according to a motion vector that points to a block of reference samples forming the predictive block, and the residual data indicates the difference between the coded block and the predictive block.
  • An intra-coded block is encoded according to an intra-coding mode and the residual data.
  • the residual data may be transformed from the pixel domain to a transform domain, resulting in residual coefficients, which then may be quantized.
  • the quantized coefficients initially arranged in a two-dimensional array, may be scanned in order to produce a one-dimensional vector of coefficients, and entropy coding may be applied to achieve even more compression.
  • Document US2015/0016501 discloses techniques for generating a current palette for a current block, according to which a video decoder first determines one or more palette entries in a predictive palette that are copied to the current palette, and then determines a number of new palette entries that are not in the predictive palette but that are included in the current palette.
  • This disclosure relates to video encoding and decoding techniques.
  • this disclosure describes techniques for encoding and decoding video data with a palette-based coding mode.
  • a palette-based coding mode pixel values for a block of video data may be coded relative to a palette of color values associated with the block of video data.
  • the palette of color values may be determined by a video encoder and may contain the color values that are most common for a particular block.
  • the video encoder may assign an index into the palette of color values to each pixel in the block of video data, and signal such an index to a video decoder in an encoded video bitstream.
  • the video decoder may then use the index into the palette to determine what color value to use for a particular pixel in the block.
  • a video encoder may also transmit the palette itself in the encoded video bitstream.
  • Techniques for transmitting the palette may include explicitly signaling the palette values, as well as predicting the palette entries for a current block from palette entries from one or more previously coded blocks. This disclosure describes techniques for coding palettes, including techniques for coding syntax elements related to palette coding and/or palette prediction.
  • a method of decoding video data comprises receiving a block of video data in an encoded video bitstream, the block of video data having been encoded using a palette-based coding mode, receiving a plurality of syntax elements that are indicative of a palette that was used to encode the block of video data, the plurality of syntax elements including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, wherein the first syntax element is encoded using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, decoding the plurality of syntax elements, including decoding the first syntax element using the one or more Golomb codes, reconstructing the palette based on the decoded plurality of syntax elements, and decoding the block of video data using the reconstructed palette.
  • a method of encoding video data comprises encoding a block of video data using a palette-based coding mode and a palette, generating a plurality of syntax elements that are indicative of the palette that was used to encode the block of video data, the plurality of syntax elements including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, encoding the first syntax element using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, and including the plurality of syntax elements in an encoded video bitstream.
  • this disclosure describes a computer-readable storage medium storing instructions that, when executed, cause one or more processors of a device configured to decode video data to receive a block of video data in an encoded video bitstream, the block of video data having been encoded using a palette-based coding mode, receive a plurality of syntax elements that are indicative of a palette that was used to encode the block of video data, the plurality of syntax elements including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, wherein the first syntax element is encoded using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, decode the plurality of syntax elements, including decoding the first syntax element using the one or more Golomb codes, reconstruct the palette based on the decoded plurality of syntax elements, and decode the block of video data using the reconstructed palette.
  • this disclosure describes a computer-readable storage medium storing instructions that, when executed, cause one or more processors of a device configured to encode video data to encode a block of video data using a palette-based coding mode and a palette, generate a plurality of syntax elements that are indicative of the palette that was used to encode the block of video data, the plurality of syntax elements including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, encode the first syntax element using one or more Golomb codes such that the length of the encoded first syntax element is less than or equal to a predetermined maximum number of bits, and include the plurality of syntax elements in an encoded video bitstream.
  • This disclosure is related to the field of video coding, and more particularly to predicting or coding a block of video data in palette-based coding mode.
  • images are assumed to be continuous-tone and spatially smooth. Based on these assumptions, various tools have been developed, such as block-based transform, filtering, etc., and such tools have shown good performance for natural content videos.
  • computer generated screen content e.g., such as text or computer graphics
  • This type of content tends to have discrete-tone, and features sharp lines and high-contrast object boundaries.
  • the assumption of continuous-tone and smoothness may no longer apply for screen content, and thus traditional video coding techniques may not be efficient to compress video data including screen content.
  • palette-based coding which may be particularly suitable for the coding of screen content.
  • a video coder e.g., a video encoder or video decoder
  • the palette may be expressed as a table of colors or pixel values representing the video data of the particular area (e.g., a given block).
  • the palette may include the most dominant pixel values in the given block. In some cases, the most dominant pixel values may include the one or more pixel values that occur most frequently within the block.
  • a video coder may apply a threshold value to determine whether a pixel value is to be included as one of the most dominant pixel values in the block.
  • the video coder may code index values indicative of one or more of the pixels values of the current block, instead of coding actual pixel values or their residuals for a current block of video data.
  • the index values indicate respective entries in the palette that are used to represent individual pixel values of the current block.
  • the video encoder may encode a block of video data by determining the palette for the block (e.g., coding the palette explicitly, predicting the palette, or a combination thereof), locating an entry in the palette to represent one or more of the pixel values, and encoding the block with index values that indicate the entry in the palette used to represent the pixel values of the block.
  • the video encoder may signal the palette and/or the index values in an encoded bitstream.
  • the video decoder may obtain, from an encoded bitstream, a palette for a block, as well as index values for the individual pixels of the block. The video decoder may relate the index values of the pixels to entries of the palette to reconstruct the various pixel values of the block.
  • this disclosure describes techniques for improving the coding efficiency when coding blocks of video data with a palette-based coding mode.
  • Examples of this disclosure include techniques for coding video data using a palette-based coding mode, and techniques for coding syntax elements related to the palette-based coding mode.
  • the techniques of this disclosure relate to coding syntax elements used by a video decoder to determine and/or reconstruct a palette for a block of video data.
  • the palette-based coding techniques of this disclosure may be configured for use with one or more video coding standards.
  • Some example video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable Video Coding (SVC) and Multiview Video Coding (MVC) extensions.
  • the palette-based coding techniques may be configured for use with the High Efficiency Video Coding (HEVC).
  • HEVC is a new video coding standard developed by the Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).
  • HEVC Joint Collaboration Team on Video Coding
  • JCT-VC Joint Collaboration Team on Video Coding
  • VCEG Video Coding Experts Group
  • MPEG ISO/IEC Motion Picture Experts Group
  • ITU-T H.265 (V1) ITU-T H.265
  • the JCT-VC is developing an extension to the HEVC standard, referred to as the HEVC Screen Content Coding (SCC) standard.
  • SCC Screen Content Coding
  • JCT-VC Joint Collaborative Team on Video Coding
  • FIG. 1 is a block diagram illustrating an example video coding system 10 that may utilize the techniques of this disclosure for palette-based video coding.
  • video coder refers generically to both video encoders and video decoders.
  • video coding or “coding” may refer generically to video encoding or video decoding.
  • Video encoder 20 and video decoder 30 of video coding system 10 represent examples of devices that may be configured to perform techniques for palette-based video coding in accordance with various examples described in this disclosure.
  • video encoder 20 and video decoder 30 may be configured to selectively code various blocks of video data, such as CUs or PUs in HEVC coding, using either palette-based coding or non-palette based coding.
  • Non-palette based coding modes may refer to various inter-predictive temporal coding modes or intra-predictive spatial coding modes, such as the various coding modes specified by the HEVC standard.
  • the techniques of this disclosure may be used with any video coding techniques and/or standards that use a palette-based coding mode.
  • video coding system 10 includes a source device 12 and a destination device 14.
  • Source device 12 generates encoded video data. Accordingly, source device 12 may be referred to as a video encoding device or a video encoding apparatus.
  • Destination device 14 may decode the encoded video data generated by source device 12. Accordingly, destination device 14 may be referred to as a video decoding device or a video decoding apparatus.
  • Source device 12 and destination device 14 may be examples of video coding devices or video coding apparatuses.
  • Source device 12 and destination device 14 may comprise a wide range of devices, including desktop computers, mobile computing devices, notebook (e.g., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called “smart" phones, televisions, cameras, display devices, digital media players, video gaming consoles, in-car computers, or the like.
  • desktop computers mobile computing devices
  • notebook (e.g., laptop) computers tablet computers
  • set-top boxes telephone handsets such as so-called “smart" phones
  • televisions cameras
  • display devices digital media players
  • video gaming consoles in-car computers, or the like.
  • Destination device 14 may receive encoded video data from source device 12 via a channel 16.
  • Channel 16 may comprise one or more media or devices capable of moving the encoded video data from source device 12 to destination device 14.
  • channel 16 may comprise one or more communication media that enable source device 12 to transmit encoded video data directly to destination device 14 in real-time.
  • source device 12 may modulate the encoded video data according to a communication standard, such as a wireless communication protocol, and may transmit the modulated video data to destination device 14.
  • the one or more communication media may include wireless and/or wired communication media, such as a radio frequency (RF) spectrum or one or more physical transmission lines.
  • RF radio frequency
  • the one or more communication media may form part of a packet-based network, such as a local area network, a wide-area network, or a global network (e.g., the Internet).
  • the one or more communication media may include routers, switches, base stations, or other equipment that facilitate communication from source device 12 to destination device 14.
  • channel 16 may include a storage medium that stores encoded video data generated by source device 12.
  • destination device 14 may access the storage medium via disk access or card access.
  • the storage medium may include a variety of locally-accessed data storage media such as Blu-ray discs, DVDs, CD-ROMs, flash memory, or other suitable digital storage media for storing encoded video data.
  • channel 16 may include a file server or another intermediate storage device that stores encoded video data generated by source device 12.
  • destination device 14 may access encoded video data stored at the file server or other intermediate storage device via streaming or download.
  • the file server may be a type of server capable of storing encoded video data and transmitting the encoded video data to destination device 14.
  • Example file servers include web servers (e.g., for a website), file transfer protocol (FTP) servers, network attached storage (NAS) devices, and local disk drives.
  • Destination device 14 may access the encoded video data through a standard data connection, such as an Internet connection.
  • a standard data connection such as an Internet connection.
  • Example types of data connections may include wireless channels (e.g., Wi-Fi connections), wired connections (e.g., DSL, cable modem, etc.), or combinations of both that are suitable for accessing encoded video data stored on a file server.
  • the transmission of encoded video data from the file server may be a streaming transmission, a download transmission, or a combination of both.
  • palette-based video coding are not limited to wireless applications or settings.
  • the techniques may be applied to video coding in support of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, streaming video transmissions, e.g., via the Internet, encoding of video data for storage on a data storage medium, decoding of video data stored on a data storage medium, or other applications.
  • video coding system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.
  • Video coding system 10 illustrated in FIG. 1 is merely one example.
  • the techniques of this disclosure may apply to video coding use cases (e.g., video encoding or video decoding) that do not necessarily include any data communication between the encoding and decoding devices.
  • data is retrieved from a local memory, streamed over a network, or the like.
  • a video encoding device may encode and store data to memory, and/or a video decoding device may retrieve and decode data from memory.
  • the encoding and decoding is performed by devices that do not communicate with one another, but simply encode data to memory and/or retrieve and decode data from memory.
  • source device 12 includes a video source 18, a video encoder 20, and an output interface 22.
  • output interface 22 may include a modulator/demodulator (modem) and/or a transmitter.
  • Video source 18 may include a video capture device, e.g., a video camera, a video archive containing previously-captured video data, a video feed interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources of video data.
  • Video encoder 20 may encode video data from video source 18.
  • source device 12 directly transmits the encoded video data to destination device 14 via output interface 22.
  • the encoded video data may also be stored onto a storage medium or a file server for later access by destination device 14 for decoding and/or playback.
  • destination device 14 includes an input interface 28, a video decoder 30, and a display device 32.
  • input interface 28 includes a receiver and/or a modem.
  • Input interface 28 may receive encoded video data over channel 16.
  • Display device 32 may be integrated with or may be external to destination device 14. In general, display device 32 displays decoded video data.
  • Display device 32 may comprise a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.
  • LCD liquid crystal display
  • OLED organic light emitting diode
  • This disclosure may generally refer to video encoder 20 "signaling" or “transmitting” certain information to another device, such as video decoder 30.
  • the term “signaling” or “transmitting” may generally refer to the communication of syntax elements and/or other data used to decode the compressed video data. Such communication may occur in real- or near-real-time. Alternately, such communication may occur over a span of time, such as might occur when storing syntax elements to a computer-readable storage medium in an encoded bitstream at the time of encoding, which then may be retrieved by a decoding device at any time after being stored to this medium.
  • video decoder 30 may be referred to as "receiving" certain information, the receiving of information does not necessarily occur in real- or near-real-time and may be retrieved from a medium at some time after storage.
  • Video encoder 20 and video decoder 30 each may be implemented as any of a variety of suitable circuitry, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, hardware, or any combinations thereof. If the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Any of the foregoing (including hardware, software, a combination of hardware and software, etc.) may be considered to be one or more processors. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device.
  • CODEC combined encoder/decoder
  • video encoder 20 and video decoder 30 operate according to a video compression standard, such as HEVC standard mentioned above.
  • HEVC high definition video Coding
  • palette-based coding modes e.g., as described in this disclosure, may be provided for extension of the HEVC standard.
  • the techniques described in this disclosure for palette-based coding may be applied to encoders and decoders configured to operation according to other video coding standards. Accordingly, application of a palette-based coding mode for coding of coding units (CUs) or prediction units (PUs) in an HEVC codec is described for purposes of example.
  • a video sequence typically includes a series of pictures. Pictures may also be referred to as "frames.”
  • a picture may include three sample arrays, denoted S L , S Cb and S Cr .
  • S L is a two-dimensional array (e.g., a block) of luma samples.
  • S Cb is a two-dimensional array of Cb chrominance samples.
  • S Cr is a two-dimensional array of Cr chrominance samples.
  • Chrominance samples may also be referred to herein as "chroma" samples.
  • a picture may be monochrome and may only include an array of luma samples.
  • video encoder 20 may generate a set of coding tree units (CTUs).
  • Each of the CTUs may be a coding tree block of luma samples, two corresponding coding tree blocks of chroma samples, and syntax structures used to code the samples of the coding tree blocks.
  • a coding tree block may be an NxN block of samples.
  • a CTU may also be referred to as a "tree block” or a "largest coding unit” (LCU).
  • the CTUs of HEVC may be broadly analogous to the macroblocks of other standards, such as H.264/AVC. However, a CTU is not necessarily limited to a particular size and may include one or more coding units (CUs).
  • a slice may include an integer number of CTUs ordered consecutively in the raster scan.
  • a coded slice may comprise a slice header and slice data.
  • the slice header of a slice may be a syntax structure that includes syntax elements that provide information about the slice.
  • the slice data may include coded CTUs of the slice.
  • video unit or “video block” or “block” to refer to one or more sample blocks and syntax structures used to code samples of the one or more blocks of samples.
  • Example types of video units or blocks may include CTUs, CUs, PUs, transform units (TUs), macroblocks, macroblock partitions, and so on.
  • discussion of PUs may be interchanged with discussion of macroblocks or macroblock partitions.
  • video encoder 20 may recursively perform quad-tree partitioning on the coding tree blocks of a CTU to divide the coding tree blocks into coding blocks, hence the name "coding tree units."
  • a coding block is an NxN block of samples.
  • a CU may be a coding block of luma samples and two corresponding coding blocks of chroma samples of a picture that has a luma sample array, a Cb sample array and a Cr sample array, and syntax structures used to code the samples of the coding blocks.
  • Video encoder 20 may partition a coding block of a CU into one or more prediction blocks.
  • a prediction block may be a rectangular (e.g., square or non-square) block of samples on which the same prediction is applied.
  • a prediction unit (PU) of a CU may be a prediction block of luma samples, two corresponding prediction blocks of chroma samples of a picture, and syntax structures used to predict the prediction block samples.
  • Video encoder 20 may generate predictive luma, Cb and Cr blocks for luma, Cb and Cr prediction blocks of each PU of the CU.
  • Video encoder 20 may use intra prediction or inter prediction to generate the predictive blocks for a PU. If video encoder 20 uses intra prediction to generate the predictive blocks of a PU, video encoder 20 may generate the predictive blocks of the PU based on decoded samples of the picture associated with the PU.
  • video encoder 20 may generate the predictive blocks of the PU based on decoded samples of one or more pictures other than the picture associated with the PU.
  • Video encoder 20 may use uni-prediction or bi-prediction to generate the predictive blocks of a PU.
  • the PU may have a single motion vector (MV).
  • MV motion vector
  • video encoder 20 uses bi-prediction to generate the predictive blocks for a PU, the PU may have two MVs.
  • video encoder 20 may generate residual blocks for the CU.
  • Each sample in a residual block of the CU may indicate a difference between a sample in a predictive block of a PU of the CU and a corresponding sample in a coding block of the CU.
  • video encoder 20 may generate a luma residual block for the CU.
  • Each sample in the CU's luma residual block indicates a difference between a luma sample in one of the CU's predictive luma blocks and a corresponding sample in the CU's original luma coding block.
  • video encoder 20 may generate a Cb residual block for the CU.
  • Each sample in the CU's Cb residual block may indicate a difference between a Cb sample in one of the CU's predictive Cb blocks and a corresponding sample in the CU's original Cb coding block.
  • Video encoder 20 may also generate a Cr residual block for the CU.
  • Each sample in the CU's Cr residual block may indicate a difference between a Cr sample in one of the CU's predictive Cr blocks and a corresponding sample in the CU's original Cr coding block.
  • video encoder 20 may use quad-tree partitioning to decompose the residual blocks (e.g., luma, Cb and Cr residual blocks) of a CU into one or more transform blocks (e.g., luma, Cb and Cr transform blocks).
  • a transform block may be a rectangular block of samples on which the same transform is applied.
  • a transform unit (TU) of a CU may be a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax structures used to transform the transform block samples.
  • each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block.
  • the luma transform block associated with the TU may be a sub-block of the CU's luma residual block.
  • the Cb transform block may be a sub-block of the CU's Cb residual block.
  • the Cr transform block may be a sub-block of the CU's Cr residual block.
  • Video encoder 20 may apply one or more transforms to a transform block to generate a coefficient block for a TU.
  • a coefficient block may be a two-dimensional array of transform coefficients.
  • a transform coefficient may be a scalar quantity.
  • video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU.
  • Video encoder 20 may apply one or more transforms to a Cb transform block of a TU to generate a Cb coefficient block for the TU.
  • Video encoder 20 may apply one or more transforms to a Cr transform block of a TU to generate a Cr coefficient block for the TU.
  • video encoder 20 may quantize the coefficient block. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression.
  • video encoder 20 may entropy encoding syntax elements indicating the quantized transform coefficients. For example, video encoder 20 may perform Context-Adaptive Binary Arithmetic Coding (CABAC) on the syntax elements indicating the quantized transform coefficients.
  • CABAC Context-Adaptive Binary Arithmetic Coding
  • Video encoder 20 may output the entropy-encoded syntax elements in a bitstream. The bitstream may also include syntax elements that are not entropy encoded.
  • Video encoder 20 may output a bitstream that includes the entropy-encoded syntax elements.
  • the bitstream may include a sequence of bits that forms a representation of coded pictures and associated data.
  • the bitstream may comprise a sequence of network abstraction layer (NAL) units.
  • NAL network abstraction layer
  • Each of the NAL units includes a NAL unit header and encapsulates a raw byte sequence payload (RBSP).
  • the NAL unit header may include a syntax element that indicates a NAL unit type code.
  • the NAL unit type code specified by the NAL unit header of a NAL unit indicates the type of the NAL unit.
  • a RBSP may be a syntax structure containing an integer number of bytes that is encapsulated within a NAL unit. In some instances, an RBSP includes zero bits.
  • NAL units may encapsulate different types of RBSPs. For example, a first type of NAL unit may encapsulate an RBSP for a picture parameter set (PPS), a second type of NAL unit may encapsulate an RBSP for a coded slice, a third type of NAL unit may encapsulate an RBSP for supplemental enhancement information (SEI), and so on.
  • NAL units that encapsulate RBSPs for video coding data (as opposed to RBSPs for parameter sets and SEI messages) may be referred to as video coding layer (VCL) NAL units.
  • VCL video coding layer
  • Video decoder 30 may receive a bitstream generated by video encoder 20.
  • video decoder 30 may obtain syntax elements from the bitstream.
  • video decoder 30 may parse the bitstream to decode syntax elements from the bitstream.
  • Video decoder 30 may reconstruct the pictures of the video data based at least in part on the syntax elements obtained (e.g., decoded) from the bitstream.
  • the process to reconstruct the video data may be generally reciprocal to the process performed by video encoder 20.
  • video decoder 30 may use MVs of PUs to determine inter-predictive sample blocks (e.g., inter-predictive blocks) for the PUs of a current CU.
  • video decoder 30 may inverse quantize transform coefficient blocks associated with TUs of the current CU. Video decoder 30 may perform inverse transforms on the transform coefficient blocks to reconstruct transform blocks associated with the TUs of the current CU. Video decoder 30 may reconstruct the coding blocks of the current CU by adding the samples of the predictive sample blocks for PUs of the current CU to corresponding samples of the transform blocks of the TUs of the current CU. By reconstructing the coding blocks for each CU of a picture, video decoder 30 may reconstruct the picture.
  • video encoder 20 and video decoder 30 may be configured to perform palette-based coding.
  • palette based coding rather than performing the intra-predictive or inter-predictive coding techniques described above, video encoder 20 and video decoder 30 may code a so-called palette as a table of colors or pixel values representing the video data of a particular area (e.g., a given block).
  • the video coder may code index values for one or more of the pixel values of the current block, where the index values indicate entries in the palette that are used to represent the pixel values of the current block (e.g., the index may map to a set of Y, Cr, and Cb values or to a set of R, G, and B values).
  • video encoder 20 may encode a block of video data by determining a palette for the block, locating an entry in the palette having a value representative of the value of one or more individual pixels of the block, and encoding the block with index values that indicate the entry in the palette used to represent the one or more individual pixel values of the block. Additionally, video encoder 20 may signal the index values in an encoded bitstream.
  • a video decoding device e.g., video decoder 30
  • Video decoder 30 may match the index values of the individual pixels to entries of the palette to reconstruct the pixel values of the block.
  • video decoder 30 may identify such an individual pixel as an escape pixel, for the purposes of palette-based coding.
  • the pixel value of an escape pixel may be encoded explicitly rather than by way of a palette index.
  • video encoder 20 may encode a block of video data according to the following operations.
  • Video encoder 20 may determine prediction residual values for individual pixels of the block, determine a palette for the block, and locate an entry (e.g., index value) in the palette having a value representative of the value of one or more of the prediction residual values of the individual pixels.
  • video encoder 20 may encode the block with index values that indicate the entry in the palette used to represent the corresponding prediction residual value for each individual pixel of the block.
  • Video decoder 30 may obtain, from an encoded bitstream signaled by source device 12, a palette for a block, as well as index values for the prediction residual values corresponding to the individual pixels of the block. As described, the index values may correspond to entries in the palette associated with the current block.
  • video decoder 30 may relate the index values of the prediction residual values to entries of the palette to reconstruct the prediction residual values of the block.
  • the prediction residual values may be added to the prediction values (for example, obtained using intra or inter prediction) to reconstruct the pixel values of the block.
  • palette-based coding may derive a palette that includes the most dominant pixel values in the current block.
  • the palette may refer to a number of pixel values which are determined or assumed to be dominant and/or representative for the current CU.
  • Video encoder 20 may first transmit the size and the elements of the palette to video decoder 30. Additionally, video encoder 20 may encode the pixel values in the given block according to a certain scanning order. For each pixel included in the given block, video encoder 20 may signal the index value that maps the pixel value to a corresponding entry in the palette.
  • video encoder 20 may encode and signal an index value that is reserved for an escape pixel, i.e., to indicate that it is an escape pixel and not a pixel for which there is an entry in the palette.
  • video encoder 20 may also encode and signal the pixel value or a residual value (or quantized versions thereof) for an escape pixel included in the given block.
  • video decoder 30 may first determine the palette based on the information received from video encoder 20. Video decoder 30 may then map the received index values associated with the pixel locations in the given block to entries of the palette to reconstruct the pixel values of the given block. In some instances, video decoder 30 may determine that a pixel of a palette-coded block is an escape pixel, such as by determining that the pixel is palette-coded with an index value reserved for escape pixels. In instances where video decoder 30 identifies an escape pixel in a palette-coded block, video decoder 30 may receive the pixel value or a residual value (or quantized versions thereof) for an escape pixel included in the given block. Video decoder 30 may reconstruct the palette-coded block by mapping the individual pixel values to the corresponding palette entries, and by using the pixel value or residual value (or quantized versions thereof) to reconstruct any escape pixels included in the palette-coded block.
  • Video encoder 20 and/or video decoder 30 may be configured to operate according to the techniques described in this disclosure, as will be described in more detail below.
  • video encoder 20 and/or video decoder 30 may be configured to encode and decode video data using one or more palette coding modes, wherein the palette coding modes do not include a palette sharing mode.
  • Techniques of this disclosure include a video coding device, such as video encoder 20, being configured to determine a first bin of a first syntax element that indicates a number of entries in a current palette that are explicitly signaled.
  • Video encoder 20 may be further configured to encode a bitstream.
  • the bitstream may include the first syntax element.
  • the bitstream also may not include a second syntax element that indicates a palette sharing mode.
  • determining the first bin of the first syntax element comprises determining the first bin of the first syntax element using a context-adaptive binary arithmetic coding. In other examples, determining the first bin of the first syntax element comprises determining the first bin of the first syntax element using one or more contexts. In some examples of using one or more contexts, the one or more contexts may be based on at least one of a predicted number of palate coding entries or a block size.
  • video encoder 20 being configured to determine that a current pixel is a first pixel in a line in a scanning order. Video encoder 20 may further determine that a neighboring pixel situated above the current pixel is available. In response to determining that the current pixel is the first pixel in the line in the scanning order and determining that the neighboring pixel situated above the current pixel is available, video encoder 20 may be further configured to bypass encoding a first syntax element in a bitstream, wherein the first syntax element indicates a run type and encode a remainder of the bitstream.
  • Video encoder 20 being configured to determine a first syntax element that indicates a maximum allowed palette size and has a minimum value of zero.
  • Video encoder 20 may also be configured to encode a bitstream that includes the first syntax element.
  • the bitstream further includes a second syntax element that indicates a maximum predictor palette size and has a minimum value of zero.
  • the first syntax element has a maximum value of 4096 and the second syntax element has a maximum value of 8192.
  • the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 4095.
  • the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 8191.
  • the first syntax element has a maximum value that is equal to a number of pixels in a largest coding unit and the second syntax element has a maximum value that is equal to a positive constant, such as 2, multiplied by the maximum value of the first syntax element.
  • the bitstream includes another syntax element that indicates a number of entries in a current palette that are explicitly signaled. In some examples of this, this syntax element is represented by one of a Golomb Rice code, an Exponential Golomb code, a Truncated Rice code, or a Unary code.
  • this syntax element is represented by one of a truncated Golomb Rice code, a truncated Exponential Golomb code, a truncated Truncated Rice code, a truncated Unary code, or a code that is also used to code a third syntax element included in the encoded bitstream that indicates whether a palette index is copied from a palette index in a row above a current pixel or is explicitly coded in the encoded bitstream.
  • this syntax element is represented by a Truncated Rice mode.
  • the syntax element that indicates a number of entries in a current palette that are explicitly signaled has a maximum value that is equal to the number of pixels in a current block of the video data.
  • this disclosure describes a video coding device, such as video decoder 30, being configured to receive an encoded bitstream.
  • the encoded bitstream does not include a first syntax element that indicates a palette sharing mode.
  • the encoded bitstream includes a second syntax element that indicates a number of entries in a current palette that are explicitly signaled.
  • Video decoder 30 may be further configured to decode a first bin of the second syntax element.
  • decoding the first bin of the second syntax element comprises decoding the first bin of the second syntax element using a context-adaptive binary arithmetic coding element.
  • decoding the first bin of the second syntax element comprises decoding the first bin of the second syntax element using one or more contexts.
  • the one or more contexts may be based on at least one of a predicted number of palate coding entries or a block size.
  • video decoder 30 being configured to receive an encoded bitstream.
  • the encoded bitstream may include a first syntax element that indicates a run type.
  • Video decoder 30 may further be configured to determine that a current pixel is a first pixel in a line in a scanning order.
  • Video decoder 30 may further determine that a neighboring pixel situated above the current pixel is available.
  • video decoder 30 may bypass decoding the first syntax element.
  • video decoder 30 being configured to receive an encoded bitstream that includes a first syntax element that indicates a maximum allowed palette size and has a minimum value of zero.
  • Video decoder 30 may be further configured to decode the encoded bitstream.
  • the encoded bitstream further includes a second syntax element that indicates a maximum predictor palette size and has a minimum value of zero.
  • the first syntax element has a maximum value of 4096 and the second syntax element has a maximum value of 8192.
  • the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 4095.
  • the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 8191.
  • the first syntax element has a maximum value that is equal to a number of pixels in a largest coding unit and the second syntax element has a maximum value that is equal to a positive constant, such as 2, multiplied by the maximum value of the first syntax element.
  • the encoded bitstream includes another syntax element that indicates a number of entries in a current palette that are explicitly signaled.
  • the syntax element that indicates a number of entries in a current palette that are explicitly signaled is represented by one of a Golomb Rice code, an Exponential Golomb code, a Truncated Rice code, or a Unary code.
  • the syntax element that indicates a number of entries in a current palette that are explicitly signaled is represented by one of a truncated Golomb Rice code, a truncated Exponential Golomb code, a truncated Truncated Rice code, a truncated Unary code, or the same code that is used to code a syntax element that indicates whether a palette index is copied from a palette index in a row above a current pixel or is explicitly coded in the encoded bitstream.
  • the syntax element that indicates a number of entries in a current palette that are explicitly signaled is represented by a Truncated Rice mode.
  • the syntax element that indicates a number of entries in a current palette that are explicitly signaled has a maximum value that is equal to the number of pixels in a current block of the video data.
  • video decoder 30 may be configured to receive a block of video data in an encoded video bitstream, the block of video data having been encoded using a palette-based coding mode, receive a plurality of syntax elements that are indicative of a palette that was used to encode the block of video data, the plurality of syntax elements including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, decode the plurality of syntax elements, including decoding the first syntax element using one or more Golomb codes, reconstruct the palette based on the decoded plurality of syntax elements, and decode the block of video data using the reconstructed palette.
  • video encoder 20 may be configured to encode a block of video data using a palette-based coding mode and a palette, generate a plurality of syntax elements that are indicative of the palette that was used to encode the block of video data, the plurality of syntax elements including a first syntax element that indicates a number of a palette values for the palette that are explicitly signaled in the encoded video bitstream, encode the first syntax element using one or more Golomb codes, and include the plurality of syntax elements in an encoded video bitstream.
  • FIG. 2 is a block diagram illustrating an example video encoder 20 that may implement various techniques of this disclosure.
  • FIG. 2 is provided for purposes of explanation and should not be considered limiting of the techniques as broadly exemplified and described in this disclosure.
  • this disclosure describes video encoder 20 in the context of HEVC coding.
  • the techniques of this disclosure may be applicable to other coding standards or methods.
  • video encoder 20 includes a video data memory 98, a prediction processing unit 100, a residual generation unit 102, a transform processing unit 104, a quantization unit 106, an inverse quantization unit 108, an inverse transform processing unit 110, a reconstruction unit 112, a filter unit 114, a decoded picture buffer 116, and an entropy encoding unit 118.
  • Prediction processing unit 100 includes an inter-prediction processing unit 120 and an intra-prediction processing unit 126.
  • Inter-prediction processing unit 120 includes a motion estimation unit and a motion compensation unit (not shown).
  • Video encoder 20 also includes a palette-based encoding unit 122 configured to perform various aspects of the palette-based coding techniques described in this disclosure. In other examples, video encoder 20 may include more, fewer, or different structural components.
  • Video data memory 98 may store video data to be encoded by the components of video encoder 20.
  • the video data stored in video data memory 98 may be obtained, for example, from video source 18 of FIG. 1 .
  • Decoded picture buffer 116 may be a reference picture memory that stores reference video data for use in encoding video data by video encoder 20, e.g., in intra- or inter-coding modes.
  • Video data memory 98 and decoded picture buffer 116 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices.
  • Video data memory 98 and decoded picture buffer 116 may be provided by the same memory device or separate memory devices.
  • video data memory 98 may be on-chip with other components of video encoder 20, or off-chip relative to those components.
  • Video encoder 20 may receive video data. Video encoder 20 may encode each CTU in a slice of a picture of the video data. Each of the CTUs may be associated with equally-sized luma coding tree blocks (CTBs) and corresponding CTBs of the picture. As part of encoding a CTU, prediction processing unit 100 may perform quad-tree partitioning to divide the CTBs of the CTU into progressively-smaller blocks. The smaller block may be coding blocks of CUs. For example, prediction processing unit 100 may partition a CTB associated with a CTU into four equally-sized sub-blocks, partition one or more of the sub-blocks into four equally-sized sub-sub-blocks, and so on.
  • CTBs luma coding tree blocks
  • Video encoder 20 may encode CUs of a CTU to generate encoded representations of the CUs (e.g., coded CUs).
  • prediction processing unit 100 may partition the coding blocks associated with the CU among one or more PUs of the CU.
  • each PU may be associated with a luma prediction block and corresponding chroma prediction blocks.
  • Video encoder 20 and video decoder 30 may support PUs having various sizes. As indicated above, the size of a CU may refer to the size of the luma coding block of the CU and the size of a PU may refer to the size of a luma prediction block of the PU.
  • video encoder 20 and video decoder 30 may support PU sizes of 2Nx2N or NxN for intra prediction, and symmetric PU sizes of 2Nx2N, 2NxN, Nx2N, NxN, or similar for inter prediction.
  • Video encoder 20 and video decoder 30 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter prediction.
  • Inter-prediction processing unit 120 may generate predictive data for a PU by performing inter prediction on each PU of a CU.
  • the predictive data for the PU may include one or more predictive sample blocks of the PU and motion information for the PU.
  • Inter-prediction processing unit 120 may perform different operations for a PU of a CU depending on whether the PU is in an I slice, a P slice, or a B slice. In an I slice, all PUs are intra predicted. Hence, if the PU is in an I slice, inter-prediction processing unit 120 does not perform inter prediction on the PU.
  • the predictive block is formed using spatial prediction from previously-encoded neighboring blocks within the same frame.
  • the motion estimation unit of inter-prediction processing unit 120 may search the reference pictures in a list of reference pictures (e.g., "RefPicListO") for a reference region for the PU.
  • the reference region for the PU may be a region, within a reference picture, that contains sample blocks that most closely correspond to the sample blocks of the PU.
  • the motion estimation unit may generate a reference index that indicates a position in RefPicListO of the reference picture containing the reference region for the PU.
  • the motion estimation unit may generate an MV that indicates a spatial displacement between a coding block of the PU and a reference location associated with the reference region.
  • the MV may be a two-dimensional vector that provides an offset from the coordinates in the current decoded picture to coordinates in a reference picture.
  • the motion estimation unit may output the reference index and the motion vector (MV) as the motion information of the PU.
  • the motion compensation unit of inter-prediction processing unit 120 may generate the predictive sample blocks of the PU based on actual or interpolated samples at the reference location indicated by the MV of the PU.
  • the motion estimation unit may perform uni-prediction or bi-prediction for the PU.
  • the motion estimation unit may search the reference pictures of RefPicListO or a second reference picture list ("RefPicList1") for a reference region for the PU.
  • the motion estimation unit may output, as the motion information of the PU, a reference index that indicates a position in RefPicListO or RefPicList1 of the reference picture that contains the reference region, an MV that indicates a spatial displacement between a sample block of the PU and a reference location associated with the reference region, and one or more prediction direction indicators that indicate whether the reference picture is in RefPicListO or RefPicList1.
  • the motion compensation unit of inter-prediction processing unit 120 may generate the predictive sample blocks of the PU based at least in part on actual (i.e., integer precision) or interpolated (i.e., fractional precision) samples at the reference region indicated by the motion vector of the PU.
  • the motion estimation unit may search the reference pictures in RefPicListO for a reference region for the PU and may also search the reference pictures in RefPicList1 for another reference region for the PU.
  • the motion estimation unit may generate reference picture indexes that indicate positions in RefPicListO and RefPicList1 of the reference pictures that contain the reference regions.
  • the motion estimation unit may generate MVs that indicate spatial displacements between the reference location associated with the reference regions and a sample block of the PU.
  • the motion information of the PU may include the reference indexes and the MVs of the PU.
  • the motion compensation unit may generate the predictive sample blocks of the PU based at least in part on actual or interpolated samples at the reference region indicated by the motion vector of the PU.
  • video encoder 20 may be configured to perform palette-based coding.
  • the palette-based coding techniques may be configured to be used as a CU mode.
  • the palette-based coding techniques may be configured to be used as a PU mode in the framework of HEVC. Accordingly, all of the disclosed processes described herein (throughout this disclosure) in the context of a CU mode may, additionally or alternatively, apply to a PU mode.
  • these HEVC-based examples should not be considered a restriction or limitation of the palette-based coding techniques described herein, as such techniques may be applied to work independently or as part of other existing or yet to be developed systems/standards.
  • the unit for palette coding can be square blocks, rectangular blocks or even regions of non-rectangular shape.
  • Palette-based encoding unit 122 may perform palette-based coding when a palette-based encoding mode is selected, e.g., for a CU or PU.
  • palette-based encoding unit 122 may be configured to generate a palette having entries indicating pixel values, select pixel values in a palette to represent pixel values of at least some positions of a block of video data, and signal information associating at least some of the positions of the block of video data with entries in the palette corresponding, respectively, to the selected pixel values.
  • various functions are described as being performed by palette-based encoding unit 122, some or all of such functions may be performed by other processing units, or a combination of different processing units.
  • Palette-based encoding unit 122 may be configured to generate any of the various syntax elements described herein related to palette-based coding. Accordingly, video encoder 20 may be configured to encode blocks of video data using palette-based code modes as described in this disclosure. Video encoder 20 may selectively encode a block of video data using a palette coding mode, or encode a block of video data using a different mode, e.g., such an HEVC inter-predictive or intra-predictive coding mode. The block of video data may be, for example, a CU or PU generated according to an HEVC coding process. A video encoder 20 may encode some blocks with inter-predictive temporal prediction or intra-predictive spatial coding modes and decode other blocks with the palette-based coding mode.
  • Intra-prediction processing unit 126 may generate predictive data for a PU by performing intra prediction on the PU.
  • the predictive data for the PU may include predictive sample blocks for the PU and various syntax elements.
  • Intra-prediction processing unit 126 may perform intra prediction on PUs in I slices, P slices, and B slices.
  • intra-prediction processing unit 126 may use multiple intra prediction modes to generate multiple sets of predictive data for the PU.
  • intra-prediction processing unit 126 may extend values of samples from sample blocks of neighboring PUs across the predictive blocks of the PU in directions associated with the intra prediction modes.
  • the neighboring PUs may be above, above and to the right, above and to the left, or to the left of the PU, assuming a left-to-right, top-to-bottom encoding order for PUs, CUs, and CTUs.
  • Intra-prediction processing unit 126 may use any of a number of different intra prediction modes, e.g., 33 directional intra prediction modes. In some examples, the number of intra prediction modes may depend on the size of the region associated with the PU.
  • Prediction processing unit 100 may select the predictive data for PUs of a CU from among the predictive data generated by inter-prediction processing unit 120 for the PUs or the predictive data generated by intra-prediction processing unit 126 for the PUs. In some examples, prediction processing unit 100 selects the predictive data for the PUs of the CU based on rate/distortion metrics of the sets of predictive data.
  • the predictive sample blocks of the selected predictive data may be referred to herein as the selected predictive sample blocks.
  • Residual generation unit 102 may generate, based on the coding blocks (e.g., luma, Cb and Cr coding blocks) of a CU and the selected predictive sample blocks (e.g., predictive luma, Cb and Cr blocks) of the PUs of the CU, residual blocks (e.g., luma, Cb and Cr residual blocks) of the CU. For instance, residual generation unit 102 may generate the residual blocks of the CU such that each sample in the residual blocks has a value equal to a difference between a sample in a coding block of the CU and a corresponding sample in a corresponding selected predictive sample block of a PU of the CU.
  • residual blocks e.g., luma, Cb and Cr residual blocks
  • Transform processing unit 104 may perform quad-tree partitioning to partition the residual blocks associated with a CU into transform blocks associated with TUs of the CU.
  • a TU may be associated with a luma transform block and two chroma transform blocks.
  • the sizes and positions of the luma and chroma transform blocks of TUs of a CU may or may not be based on the sizes and positions of prediction blocks of the PUs of the CU.
  • a quad-tree structure known as a "residual quad-tree" (RQT) may include nodes associated with each of the regions.
  • the TUs of a CU may correspond to leaf nodes of the RQT.
  • Transform processing unit 104 may generate transform coefficient blocks for each TU of a CU by applying one or more transforms to the transform blocks of the TU. Transform processing unit 104 may apply various transforms to a transform block associated with a TU. For example, transform processing unit 104 may apply a discrete cosine transform (DCT), a directional transform, or a conceptually similar transform to a transform block. In some examples, transform processing unit 104 does not apply transforms to a transform block. In such examples, the transform block may be treated as a transform coefficient block.
  • DCT discrete cosine transform
  • Quantization unit 106 may quantize the transform coefficients in a coefficient block. The quantization process may reduce the bit depth associated with some or all of the transform coefficients. For example, an n-bit transform coefficient may be rounded down to an m-bit transform coefficient during quantization, where n is greater than m.
  • Quantization unit 106 may quantize a coefficient block associated with a TU of a CU based on a quantization parameter (QP) value associated with the CU.
  • QP quantization parameter
  • Video encoder 20 may adjust the degree of quantization applied to the coefficient blocks associated with a CU by adjusting the QP value associated with the CU. Quantization may introduce loss of information, thus quantized transform coefficients may have lower precision than the original ones.
  • Inverse quantization unit 108 and inverse transform processing unit 110 may apply inverse quantization and inverse transforms to a coefficient block, respectively, to reconstruct a residual block from the coefficient block.
  • Reconstruction unit 112 may add the reconstructed residual block to corresponding samples from one or more predictive sample blocks generated by prediction processing unit 100 to produce a reconstructed transform block associated with a TU. By reconstructing transform blocks for each TU of a CU in this way, video encoder 20 may reconstruct the coding blocks of the CU.
  • Filter unit 114 may perform one or more deblocking operations to reduce blocking artifacts in the coding blocks associated with a CU.
  • Decoded picture buffer 116 may store the reconstructed coding blocks after filter unit 114 performs the one or more deblocking operations on the reconstructed coding blocks.
  • Inter-prediction processing unit 120 may use a reference picture that contains the reconstructed coding blocks to perform inter prediction on PUs of other pictures.
  • intra-prediction processing unit 126 may use reconstructed coding blocks in decoded picture buffer 116 to perform intra prediction on other PUs in the same picture as the CU.
  • Entropy encoding unit 118 may receive data from other functional components of video encoder 20. For example, entropy encoding unit 118 may receive coefficient blocks from quantization unit 106 and may receive syntax elements from prediction processing unit 100. Entropy encoding unit 118 may perform one or more entropy encoding operations on the data to generate entropy-encoded data.
  • entropy encoding unit 118 may perform a CABAC operation, a context-adaptive variable length coding (CAVLC) operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a Probability Interval Partitioning Entropy (PIPE) coding operation, an Exponential-Golomb encoding operation, or another type of entropy encoding operation on the data.
  • Video encoder 20 may output a bitstream that includes entropy-encoded data generated by entropy encoding unit 118.
  • the bitstream may include data that represents a RQT for a CU.
  • residual coding is not performed with palette coding. Accordingly, video encoder 20 may not perform transformation or quantization when coding using a palette coding mode. In addition, video encoder 20 may entropy encode data generated using a palette coding mode separately from residual data.
  • video encoder 20, and specifically palette-based encoding unit 122 may perform palette-based video coding of predicted video blocks.
  • a palette generated by video encoder 20 may be explicitly encoded and sent to video decoder 30, predicted from previous palette entries, predicted from previous pixel values, or a combination thereof.
  • palette-based encoding unit 122 may apply techniques of this disclosure to perform sample value to index conversion to encode video data using one or more palette coding modes, wherein the palette coding modes do not include a palette sharing mode.
  • Techniques of this disclosure include palette-based encoding unit 122 of video encoder 20, being configured to determine a first bin of a first syntax element that indicates a number of entries in a current palette that are explicitly signaled.
  • Palette-based encoding unit 122 of video encoder 20 may be further configured to encode a bitstream.
  • the bitstream may include the first syntax element.
  • the bitstream also may not include a second syntax element that indicates a palette sharing mode.
  • determining the first bin of the first syntax element comprises determining the first bin of the first syntax element using a context-adaptive binary arithmetic coding. In other examples, determining the first bin of the first syntax element comprises determining the first bin of the first syntax element using one or more contexts. In some examples of using one or more contexts, the one or more contexts may be based on at least one of a predicted number of palette coding entries or a block size.
  • palette-based encoding unit 122 of video encoder 20 being configured to determine that a current pixel is a first pixel in a line in a scanning order. Palette-based encoding unit 122 of video encoder 20 may further determine that a neighboring pixel situated above the current pixel is available. In response to determining that the current pixel is the first pixel in the line in the scanning order and determining that the neighboring pixel situated above the current pixel is available, palette-based encoding unit 122 of video encoder 20 may be further configured to bypass encoding a first syntax element in a bitstream, wherein the first syntax element indicates a run type, and encode a remainder of the bitstream.
  • palette-based encoding unit 122 of video encoder 20 being configured to determine a first syntax element that indicates a maximum allowed palette size and has a minimum value of zero.
  • Palette-based encoding unit 122 of video encoder 20 may also be configured to encode a bitstream that includes the first syntax element.
  • the bitstream further includes a second syntax element that indicates a maximum predictor palette size and has a minimum value of zero.
  • the first syntax element has a maximum value of 4096 and the second syntax element has a maximum value of 8192.
  • the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 4095.
  • the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 8191.
  • the first syntax element has a maximum value that is equal to a number of pixels in a largest coding unit and the second syntax element has a maximum value that is equal to a positive constant, such as 2, multiplied by the maximum value of the first syntax element.
  • the bitstream includes another syntax element that indicates a number of entries in a current palette that are explicitly signaled. In some examples of this, this syntax element is represented by one of a Golomb Rice code, an Exponential Golomb code, a Truncated Rice code, or a Unary code.
  • this syntax element is represented by one of a truncated Golomb Rice code, a truncated Exponential Golomb code, a truncated Truncated Rice code, a truncated Unary code, or a code that is also used to code a third syntax element included in the encoded bitstream that indicates whether a palette index is copied from a palette index in a row above a current pixel or is explicitly coded in the encoded bitstream.
  • this syntax element is represented by a Truncated Rice mode.
  • the syntax element that indicates a number of entries in a current palette that are explicitly signaled has a maximum value that is equal to the number of pixels in a current block of the video data.
  • FIG. 3 is a block diagram illustrating an example video decoder 30 that is configured to implement the techniques of this disclosure.
  • Video decoder 30 may operate in a reciprocal manner to that of video encoder 20 described with reference to FIG. 2 .
  • FIG. 3 is provided for purposes of explanation and is not limiting on the techniques as broadly exemplified and described in this disclosure.
  • this disclosure describes video decoder 30 in the context of HEVC coding.
  • the techniques of this disclosure may be applicable to other coding standards or methods where palette mode coding is used.
  • video decoder 30 includes a video data memory 148, an entropy decoding unit 150, a prediction processing unit 152, an inverse quantization unit 154, an inverse transform processing unit 156, a reconstruction unit 158, a filter unit 160, and a decoded picture buffer 162.
  • Prediction processing unit 152 includes a motion compensation unit 164 and an intra-prediction processing unit 166.
  • Video decoder 30 also includes a palette-based decoding unit 165 configured to perform various aspects of the palette-based coding techniques described in this disclosure. In other examples, video decoder 30 may include more, fewer, or different structural components.
  • Video data memory 148 may store video data, such as an encoded video bitstream, to be decoded by the components of video decoder 30.
  • the video data stored in video data memory 148 may be obtained, for example, from channel 16, e.g., from a local video source, such as a camera, via wired or wireless network communication of video data, or by accessing physical data storage media.
  • Video data memory 148 may form a coded picture buffer (CPB) that stores encoded video data from an encoded video bitstream.
  • Decoded picture buffer 162 may be a reference picture memory that stores reference video data for use in decoding video data by video decoder 30, e.g., in intra- or inter-coding modes.
  • Video data memory 148 and decoded picture buffer 162 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. Video data memory 148 and decoded picture buffer 162 may be provided by the same memory device or separate memory devices. In various examples, video data memory 148 may be on-chip with other components of video decoder 30, or off-chip relative to those components.
  • DRAM dynamic random access memory
  • SDRAM synchronous DRAM
  • MRAM magnetoresistive RAM
  • RRAM resistive RAM
  • Video data memory 148 may receive and store encoded video data (e.g., NAL units) of a bitstream.
  • Entropy decoding unit 150 may receive encoded video data (e.g., NAL units) from video data memory 148 and may parse the NAL units to decode syntax elements.
  • Entropy decoding unit 150 may entropy decode entropy-encoded syntax elements in the NAL units.
  • Prediction processing unit 152, inverse quantization unit 154, inverse transform processing unit 156, reconstruction unit 158, and filter unit 160 may generate decoded video data based on the syntax elements obtained (e.g., extracted) from the bitstream.
  • the NAL units of the bitstream may include coded slice NAL units.
  • entropy decoding unit 150 may extract and entropy decode syntax elements from the coded slice NAL units.
  • Each of the coded slices may include a slice header and slice data.
  • the slice header may contain syntax elements pertaining to a slice.
  • the syntax elements in the slice header may include a syntax element that identifies a PPS associated with a picture that contains the slice.
  • video decoder 30 may perform a reconstruction operation on a non-partitioned CU. To perform the reconstruction operation on a non-partitioned CU, video decoder 30 may perform a reconstruction operation on each TU of the CU. By performing the reconstruction operation for each TU of the CU, video decoder 30 may reconstruct residual blocks of the CU.
  • inverse quantization unit 154 may inverse quantize, e.g., de-quantize, coefficient blocks associated with the TU.
  • Inverse quantization unit 154 may use a QP value associated with the CU of the TU to determine a degree of quantization and, likewise, a degree of inverse quantization for inverse quantization unit 154 to apply. That is, the compression ratio, e.g., the ratio of the number of bits used to represent original sequence and the compressed one, may be controlled by adjusting the value of the QP used when quantizing transform coefficients.
  • the compression ratio may also depend on the method of entropy coding employed.
  • inverse transform processing unit 156 may apply one or more inverse transforms to the coefficient block in order to generate a residual block associated with the TU.
  • inverse transform processing unit 156 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the coefficient block.
  • KLT Karhunen-Loeve transform
  • intra-prediction processing unit 166 may perform intra prediction to generate predictive blocks for the PU.
  • Intra-prediction processing unit 166 may use an intra-prediction mode to generate the predictive luma, Cb and Cr blocks for the PU based on the prediction blocks of spatially-neighboring PUs.
  • Intra-prediction processing unit 166 may determine the intra prediction mode for the PU based on one or more syntax elements decoded from the bitstream.
  • Prediction processing unit 152 may construct a first reference picture list (RefPicListO) and a second reference picture list (RefPicList1) based on syntax elements extracted from the bitstream. Furthermore, if a PU is encoded using inter prediction, entropy decoding unit 150 may extract motion information for the PU. Motion compensation unit 164 may determine, based on the motion information of the PU, one or more reference regions for the PU. Motion compensation unit 164 may generate, based on samples blocks at the one or more reference blocks for the PU, predictive blocks (e.g., predictive luma, Cb and Cr blocks) for the PU.
  • predictive blocks e.g., predictive luma, Cb and Cr blocks
  • Reconstruction unit 158 may use the transform blocks (e.g., luma, Cb and Cr transform blocks) associated with TUs of a CU and the predictive blocks (e.g., luma, Cb and Cr blocks) of the PUs of the CU, e.g., either intra-prediction data or inter-prediction data, as applicable, to reconstruct the coding blocks (e.g., luma, Cb and Cr coding blocks) of the CU.
  • the transform blocks e.g., luma, Cb and Cr transform blocks
  • the predictive blocks e.g., luma, Cb and Cr blocks
  • reconstruction unit 158 may add samples of the transform blocks (e.g., luma, Cb and Cr transform blocks) to corresponding samples of the predictive blocks (e.g., predictive luma, Cb and Cr blocks) to reconstruct the coding blocks (e.g., luma, Cb and Cr coding blocks) of the CU.
  • transform blocks e.g., luma, Cb and Cr transform blocks
  • predictive blocks e.g., predictive luma, Cb and Cr blocks
  • Filter unit 160 may perform a deblocking operation to reduce blocking artifacts associated with the coding blocks (e.g., luma, Cb and Cr coding blocks) of the CU.
  • Video decoder 30 may store the coding blocks (e.g., luma, Cb and Cr coding blocks) of the CU in decoded picture buffer 162.
  • Decoded picture buffer 162 may provide reference pictures for subsequent motion compensation, intra prediction, and presentation on a display device, such as display device 32 of FIG. 1 .
  • video decoder 30 may perform, based on the blocks (e.g., luma, Cb and Cr blocks) in decoded picture buffer 162, intra prediction or inter prediction operations on PUs of other CUs.
  • video decoder 30 may extract, from the bitstream, transform coefficient levels of a significant coefficient block, inverse quantize the transform coefficient levels, apply a transform to the transform coefficient levels to generate a transform block, generate, based at least in part on the transform block, a coding block, and output the coding block for display.
  • video decoder 30 may be configured to perform palette-based coding.
  • Palette-based decoding unit 165 may perform palette-based decoding when a palette-based decoding mode is selected, e.g., for a CU or PU.
  • palette-based decoding unit 165 may be configured to generate a palette having entries indicating pixel values.
  • palette-based decoding unit 165 may receive information associating at least some positions of a block of video data with entries in the palette.
  • palette-based decoding unit 165 may select pixel values in the palette based on the information.
  • palette-based decoding unit 165 may reconstruct pixel values of the block based on the selected pixel values. Although various functions are described as being performed by palette-based decoding unit 165, some or all of such functions may be performed by other processing units, or a combination of different processing units.
  • palette-based decoding unit 165 may receive palette coding mode information, and perform the above operations when the palette coding mode information indicates that the palette coding mode applies to the block.
  • palette-based decoding unit 165 decodes the block of video data using a non-palette based coding mode, e.g., such an HEVC inter-predictive or intra-predictive coding mode, when the palette coding mode information indicates that the palette coding mode does not apply to the block.
  • the block of video data may be, for example, a CU or PU generated according to an HEVC coding process.
  • a video decoder 30 may decode some blocks with inter-predictive temporal prediction or intra-predictive spatial coding modes and decode other blocks with the palette-based coding mode.
  • the palette-based coding mode may comprise one of a plurality of different palette-based coding modes, or there may be a single palette-based coding mode.
  • video decoder 30, and specifically palette-based decoding unit 165 may perform palette-based video decoding of palette-coded video blocks.
  • a palette decoded by video decoder 30 may be explicitly encoded and signaled by video encoder 20, reconstructed by video decoder 30 with respect to a received palette-coded block, predicted from previous palette entries, predicted from previous pixel values, or a combination thereof.
  • Palette-based decoding unit 165 may apply techniques of this disclosure to perform sample value to index conversion decode video data using one or more palette coding modes, wherein the palette coding modes do not include a palette sharing mode. Further, techniques of this disclosure include palette-based decoding unit 165 of video decoder 30 being configured to receive an encoded bitstream. In this example, the encoded bitstream does not include a first syntax element that indicates a palette sharing mode. Further, the encoded bitstream includes a second syntax element that indicates a number of entries in a current palette that are explicitly signaled. Palette-based decoding unit 165 of video decoder 30 may be further configured to decode a first bin of the second syntax element.
  • decoding the first bin of the second syntax element comprises decoding the first bin of the second syntax element using a context-adaptive binary arithmetic coding (CABAC) unit.
  • decoding the first bin of the second syntax element comprises decoding the first bin of the second syntax element using one or more contexts.
  • the one or more contexts may be based on at least one of a predicted number of palate coding entries or a block size.
  • palette-based decoding unit 165 of video decoder 30 being configured to receive an encoded bitstream.
  • the encoded bitstream may include a first syntax element that indicates a run type.
  • Palette-based decoding unit 165 of video decoder 30 may further be configured to determine that a current pixel is a first pixel in a line in a scanning order.
  • Palette-based decoding unit 165 of video decoder 30 may further determine that a neighboring pixel situated above the current pixel is available.
  • palette-based decoding unit 165 of video decoder 30 may bypass decoding the first syntax element.
  • palette-based decoding unit 165 of video decoder 30 being configured to receive an encoded bitstream that includes a first syntax element that indicates a maximum allowed palette size and has a minimum value of zero.
  • Palette-based decoding unit 165 of video decoder 30 may be further configured to decode the encoded bitstream.
  • the encoded bitstream further includes a second syntax element that indicates a maximum predictor palette size and has a minimum value of zero.
  • the first syntax element has a maximum value of 4096 and the second syntax element has a maximum value of 8192.
  • the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 4095.
  • the first syntax element has a maximum value of 4095 and the second syntax element has a maximum value of 8191.
  • the first syntax element has a maximum value that is equal to a number of pixels in a largest coding unit and the second syntax element has a maximum value that is equal to a positive constant, such as 2, multiplied by the maximum value of the first syntax element.
  • the encoded bitstream includes another syntax element, e.g., a third syntax element that indicates a number of entries in a current palette that are explicitly signaled.
  • the syntax element that indicates a number of entries in a current palette that are explicitly signaled is represented by one of a Golomb Rice code, an Exponential Golomb code, a Truncated Rice code, or a Unary code.
  • the syntax element that indicates a number of entries in a current palette that are explicitly signaled is represented by one of a truncated Golomb Rice code, a truncated Exponential Golomb code, a truncated Truncated Rice code, a truncated Unary code, or a code that is also used to code a third syntax element included in the encoded bitstream that indicates whether a palette index is copied from a palette index in a row above a current pixel or is explicitly coded in the encoded bitstream.
  • the syntax element that indicates a number of entries in a current palette that are explicitly signaled is represented by a Truncated Rice mode.
  • the syntax element that indicates a number of entries in a current palette that are explicitly signaled has a maximum value that is equal to the number of pixels in a current block of the video data.
  • video encoder 20 FIGS. 1 and 2
  • video decoder 30 FIGS. 1 and 3
  • video coding may refer to video encoding or video decoding, as applicable.
  • the palette-based coding techniques may be configured for use in one or more coding modes of the HEVC standard or the HEVC SCC standard. In other examples, the palette-based coding techniques can be used independently or as part of other existing or future systems or standards. In some examples, the techniques for palette-based coding of video data may be used with one or more other coding techniques, such as techniques for inter-predictive coding or intra-predictive coding of video data. For example, as described in greater detail below, an encoder or decoder, or combined encoder-decoder (codec), may be configured to perform inter- and intra-predictive coding, as well as palette-based coding.
  • codec combined encoder-decoder
  • the palette-based coding techniques may be configured to be used as a coding unit (CU) mode.
  • the palette-based coding techniques may be configured to be used as a prediction unit (PU) mode in the framework of HEVC. Accordingly, all of the following disclosed processes described in the context of a CU mode may, additionally or alternatively, apply to PU.
  • these HEVC-based examples should not be considered a restriction or limitation of the palette-based coding techniques described herein, as such techniques may be applied to work independently or as part of other existing or yet to be developed systems/standards.
  • the unit for palette coding can be square blocks, rectangular blocks or even regions of non-rectangular shape.
  • palette-based coding For each CU, a palette is derived which comprises (and may consist of) the most dominant pixel values in the current CU.
  • the size and the elements of the palette are first transmitted from a video encoder to a video decoder.
  • the size and/or the elements of the palette can be directly coded or predictively coded using the size and/or the elements of the palette in the neighboring CUs (e.g. above and/or left coded CU).
  • the pixel values in the CU are encoded based on the palette according to a certain scanning order.
  • a flag e.g., palette flag, is first transmitted to indicate whether the pixel value is included in the palette.
  • such a flag is called a copy_above_palette_indices_flag.
  • the palette index associated with that entry is signaled for the given pixel location in the CU.
  • a special index may be assigned to the pixel and the actual pixel value (in some cases, a quantized pixel value) is transmitted for the given pixel location in the CU.
  • These pixels are referred to as "escape pixels.”
  • An escape pixel can be coded using any existing entropy coding method such as fixed length coding, unary coding, etc.
  • no flag is used to explicitly indicate whether a pixel is an "escape" pixel.
  • a flag or other syntax element may be used to indicate a run type.
  • the syntax element indicating the run type may indicate whether the following indices are copied from the position above the current pixel or if there is a run of signaled index values. If the derived index value of a particular pixel corresponds to an "escape index" (e.g., a predetermined index in the palette indicating the use of an escape pixel), then video decoder 30 may determine that such a pixel is an escape pixel.
  • JCTVC-S0114 Kim, J., et al., "CE6-related: Enabling copy above mode prediction at the boundary of CU,” Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 19th Meeting: France, FR, 17-24 October 2014
  • JCTVC-S0120 Ye, J., et al., “Non-CE6: Copy previous mode”
  • JCTVC-S0151 Wang, W., et al., "Non-CE6: 2-D Index Map Coding of Palette Mode in HEVC SCC” Joint Collaborative Team
  • a histogram-based algorithm is used to classify the pixels.
  • the most significant N peak values in a histogram are selected as major colors for coding.
  • the pixel values that are close to a major color will be quantized to the major color.
  • Other pixels that do not belong to any major color sets are escape pixels, which are also quantized before coding. For lossless coding, no quantization is used.
  • pixels of a coding unit can be converted into color indices. After that, the major color number and values are coded. Then, the color indices are coded as follows:
  • a palette-based coding mode is included as a CU mode.
  • the encoding process of the second method may include the following:
  • the palette may make up a relatively significant portion of the bits for a palette coded block (e.g., CU). Accordingly, the video coder may predict one or more entries of the palette based on one or more entries of a previously coded palette (e.g., as noted above with respect to the "transmission of the palette").
  • the video coder may generate a palette predictor list when predicting palette entries.
  • a palette predictor list when predicting palette entries.
  • the document C. Gisquet, G. Laroche, and P. Onno, "AhG10: Palette predictor stuffing," JCTVC-Q0063 discloses one example process for determining palette predictors.
  • the video coder may use a Boolean vector to indicate whether each item in a palette predictor list is used (or not used) for predicting one or more entries in the palette for the block currently being coded.
  • all of the items in the palette predictor list are derived from the previously-coded palette (e.g., the palette coded with the previously coded block).
  • palettes may be spatially far away from the current CU, which may make the palette correlation relatively weak.
  • expanding the palette predictor table may be helpful (e.g., may provide more accurate predictors, which may result in an efficiency gain).
  • determining and using a relatively large palette predictor table results in a relatively longer Boolean vector.
  • video encoder 20 may generate a syntax element, such as a flag "PLT_Mode_flag," that indicates whether or not a palette-based coding mode is used for a particular region of a video frame.
  • the PLT_Mode_flag may be generated at the slice level, the CU-level, the PU-level, or any other level of a video frame.
  • video encoder 20 may generate the PLT_Mode_flag at the CU level and signal the PLT_Mode_flag in an encoded video bitstream.
  • Video decoder 30 may then parse the PLT_Mode_flag upon decoding the encoded video bitstream.
  • a value of this PLT_Mode_flag 1 specifies that the current CU is encoded using a palette mode.
  • video decoder 30 may apply the palette-based coding mode to decode the CU.
  • a syntax element may indicate one of a plurality of different palette modes for the CU.
  • a value of this PLT_Mode_flag specifies that the current CU is encoded using a mode other than palette mode.
  • a mode other than palette mode For example, any of a variety of inter-predictive, intra-predictive, or other coding modes may be used.
  • PLT_Mode_flag When a value of PLT_Mode_flag is 0, further information may be transmitted to signal which specific mode is used for encoding the respective CU, where such specific mode, typically, may be an HEVC coding mode (e.g., intra coding or inter coding).
  • the use of the PLT_Mode_flag is described for purposes of example. In other examples, however, other syntax elements such as multi-bit codes may be used to indicate whether the palette-based coding mode is to be used for a CU (or PU in other examples) or to indicate which of a plurality of modes are to be used.
  • the PLT_Mode_flag or other syntax element may also be transmitted at a higher level.
  • the PLT_Mode_flag may be transmitted at slice level.
  • a value of the flag equal to 1 implies that all of the CUs in the slice will be encoded using palette mode (which means no mode information, e.g., for palette mode or other modes, needs to be transmitted at CU level).
  • this flag can be signaled at the picture parameter set (PPS), sequence parameter set (SPS) or video parameter set (VPS) level.
  • a flag can be sent at one of these levels specifying whether the palette mode is enabled or disabled for the particular picture, slice, etc., while the PLT_Mode_flag indicates whether the palette-based coding mode is used for each CU.
  • the PLT_Mode_flag indicates whether the palette-based coding mode is used for each CU.
  • a flag or other syntax element sent at the slice, PPS, SPS or VPS level indicates that palette coding mode is disabled, in some examples, there may be no need to signal the PLT_Mode_flag for each CU.
  • the PLT_Mode_flag may be further signaled to indicate whether the palette-based coding mode is to be used for each CU.
  • a flag such as PLT_Mode_flag, may also or alternatively be conditionally transmitted or inferred.
  • the conditions for transmitting the PLT_Mode_flag or inferring the flag can be one or more of, as examples, the size of the CU, the frame type, the color space, the color component, the frame size, the frame rate, the layer id in scalable video coding or the view id in multi-view coding.
  • Video encoder 20 may be configured to generate and signal one or more syntax elements and values that may be used by video decoder 30 to construct and/or reconstruct the palette used by video encoder 20 to encode a particular level of the video frame (e.g., a CU).
  • video encoder 20 may indicate or otherwise signal a palette for each CU.
  • video encoder 20 may indicate or otherwise signal a palette that may be shared among several CUs.
  • the size of the palette can be a fixed value or can be signaled by video encoder 20 in an encoded video bitstream.
  • Video decoder 30 may receive and decode the indication of the palette size from the encoded video bitstream.
  • the signaling can be separate for different components or a single size can be signaled for all the components.
  • the different components may be, for example, luma and chroma components.
  • the signaling can use unary codes or truncated unary codes (e.g., that truncates at a maximum limit of the palette size). Exponential-Golomb or Rice-Golomb codes can also be used.
  • the signaling of the size can be done in the following way: after signaling an entry in the palette, a "stop" flag is signaled. A value of this flag equal to 1 specifies that the current entry is the last one in the palette; a value of this flag equal to 0 specifies that there are more entries in the palette.
  • the "stop" flag may not be transmitted by the encoder if the already constructed palette hits the maximum limit of the palette size.
  • the size of the palette can also be conditionally transmitted or inferred based on side information in the same way as described above for "Transmission of flag PLT_Mode_flag.”
  • the palette can be transmitted separately for each color component in the CU.
  • the entry may (assumedly) be a representative Y value in this CU.
  • the palette may be transmitted for all of the color components in the CU.
  • the i-th entry in the palette is a triple (Yi, Ui, Vi).
  • the palette includes values for each of the components.
  • palette prediction techniques may be used in conjunction with palette signaling techniques. That is, video encoder 20 may be configured to signal syntax elements that may be used by video decoder 30 to predict a portion of the total number of palette entries. In addition, video encoder 20 may be configured to explicitly signal another portion of the palette entries.
  • one flag "pred_palette_flag" is transmitted.
  • a value of this flag equal to 1 specifies that the palette for the current CU will be predicted from past data and thus there is no need for the palette to be transmitted.
  • a value of this flag equal to 0 means that the palette of the current CU needs to be transmitted.
  • the flag can be separate for different color components (e.g., so that 3 flags need to be transmitted for a CU in YUV video), or a single flag can be signaled for all the color components. For example, a single flag may indicate whether the palettes are transmitted for all of the components or whether the palettes for all of the components will be predicted.
  • the prediction can be performed in the following manner. If the prediction flag value is equal to 1, for the current CU, video encoder 20 copies the palette of one or more of the already encoded neighboring CUs.
  • the palette of the already encoded neighboring CUs may have been transmitted or predicted.
  • the copied neighboring CU can be the left neighboring CU. In the case that the palette of the left CU is not available (as in the case in which the left CU is not encoded using the palette mode or the current CU is at the first column of the picture), the copy of the palette can be from the CU above the current CU.
  • the copied palette can also be a combination of the palettes of a number of neighboring CUs. For example, one or more formulas, functions, rules or the like may be applied to generate a palette based on palettes of one or a combination of a plurality of neighboring CUs.
  • a candidate list may be constructed and an index is transmitted by video encoder 20 to indicate the candidate CU from which the current CU copies the palette.
  • Video decoder 30 may construct the same candidate list and then use the index to select the palette of the corresponding CU for use with the current CU.
  • the candidate list may include one CU above and one CU on the left, relative to the current CU to be coded within a slice or picture.
  • a flag or other syntax element may be signaled to indicate the candidate selection. For example, a transmitted flag equal to 0 means the copy is from the left CU, and a transmitted flag equal to 1 means the copy is from the top CU.
  • Video decoder 30 selects the palette to be copied from the corresponding neighbor CU and copies it for use in decoding the current CU. The prediction can also be derived using the most frequent sample values in the causal neighbors of the current CU.
  • the prediction of palettes can also be entry-wise. For each entry in the palette, video encoder 20 generates and signals a flag. A value of a flag equal to 1 for a given entry specifies that a predicted value (for example, the corresponding entry from a selected candidate CU like the left CU) is used as the value of this entry. A value of a flag equal to 0 specifies that this entry is not predicted and its value will be transmitted to video decoder 30 from video encoder 20, e.g., signaled in a bitstream encoded by video encoder 20 for later decoding by video decoder 30.
  • pred_palette_flag the candidate CU whose palette is used to predict the palette of the current CU or the rules for constructing the candidates, can be also conditionally transmitted or inferred based on side information in the same way as described above for "Transmission of flag PLT Mode flag.”
  • video encoder 20 may generate and signal a map which indicates what respective palette entry is associated with each pixel in a CU.
  • the i-th entry in the map is corresponding to the i-th position in the CU.
  • a value of the i-th entry equal to 1 specifies that the pixel value at this i-th location in the CU is one of the values in the palette, and a palette index is further transmitted so that video decoder 30 can reconstruct the pixel value (in case there is only one entry in the palette, the transmission of palette index may be skipped).
  • a value of the i-th entry equal to 0 specifies that the pixel value at the i-th position in the CU is not in the palette and thus the pixel value will be transmitted to video decoder 30 explicitly.
  • the value of the run may be a constant, for example, 4, 8, 16, etc., or the value of the run may also be dependent on side information.
  • the value of the run may depend on block size, e.g., the run is equal to the width of the current block, or the height of the current block, or the half-width (or half-height) of the current block, or a fraction of the width and the height of the block, or a multiple of the height/width of the block.
  • the value of the run may also be dependent on the QP, frame-type, color component, color format (e.g., 444, 422, 420) and/or color space (e.g., YUV, RGB).
  • the value of the run may also depend on the scan direction. In other examples, the value of the run may depend on other types of side information.
  • the value of the run may also be signaled using high level syntax (e.g., PPS, SPS).
  • the map may not need to be transmitted.
  • the run may only start at certain locations. For example, the run may only start at the beginning of each row, or the beginning of every N rows.
  • the starting location may be different for different scan directions. For example, if the vertical scan is used, the run may only start at the beginning of a column or the beginning of every N columns.
  • the start location may depend on side information. For example, the start location may be the mid-point of each row, or each column, or 1/n, 2/n, ... (n-1)/n (i.e., fractions) of each row/column.
  • the start location may also depend on the QP, frame-type, color component, color format (e.g., 444, 422, 420) and/or color space (e.g., YUV, RGB).
  • the start position of the run may depend on other types of side information.
  • the start position can also be signaled using high level syntax (e.g., PPS, SPS, etc.).
  • the implicit start position derivation and the implicit run derivation are combined.
  • the run is equal to the distance between two neighboring start positions.
  • the start point is the beginning (i.e., the first position) of every row
  • the length of the run is a row.
  • the scan direction may be vertical or horizontal. It is possible that a flag is transmitted for each CU to indicate the scan direction. Flags may be transmitted separately for each component or a single flag may be transmitted and the indicated scan direction applies to all the color components. It is also possible that other scan directions, like 45 degree or 135 degree, are used. The scan order may be fixed or may be dependent on side information in the same way as described above for "Transmission of flag PLT Mode flag".
  • video decoder 30 when video decoder 30 receives a new pixel value (e.g., signaled by the encoder) for a position in the CU, it includes the pixel value in the palette constructed by video decoder 30. When later positions in the CU have pixel values that have been added to the palette, video decoder 30 may receive information such as, e.g., index values, that identify the corresponding pixel values in the palette for reconstruction of the pixel values in the CU.
  • information such as, e.g., index values
  • the encoder and decoder share the same mechanism to remove an entry of the palette.
  • One method is to remove the oldest entry in the palette (FIFO queue).
  • Another method is to remove the least used entry in the palette.
  • Another is to weight both methods (time in palette and usage frequency) to decide the entry to be replaced.
  • the encoder may transmit the pixel value instead of including an entry in the palette. Additionally, or alternatively, it is possible that such a pixel value could be re-entered into the palette after having been removed, e.g., as the encoder and decoder scan the positions in the CU.
  • the initial palette would be updated with the coding of the pixels.
  • video encoder 20 may add values to the initial palette or change values in the initial palette as pixel values of additional locations in the CU are scanned.
  • video decoder 30 may add values to the initial palette or change values in the initial palette as pixel values of additional locations in the CU are scanned.
  • the encoder can signal whether the current CU uses transmission of the entire palette, or on-the-fly palette generation, or a combination of transmission of an initial palette with updating of the initial palette by on-the-fly derivation.
  • the initial palette may be a full palette at maximum palette size, in which case values in the initial palette may be changed, or a reduced size palette, in which case values are added to the initial palette and, optionally values in the initial palette are changed.
  • the transmission of the map can be done by signaling line copying.
  • line copying is signaled by video encoder 20 such that the pixel value for an entry is equal to the pixel value of the entry of a line above (or in column on the left if the scan is vertical). Then, the 'run' of entries that are copied from the line may be signaled. Also, the line from which it is copied can be indicated; several lines above may be buffered for this purpose.
  • the previous four rows are stored and which row is copied may be signaled with a truncated unary code or other codes, and then, how many entries of that row are copied, i.e., the run, may be signaled.
  • the pixel value for an entry may be signaled to be equal to a pixel value of an entry in a row immediately above or two or more rows above the current row.
  • the value of the run may be constant/fixed or may be dependent on side information (and derived by the decoder) using the method described above.
  • the run may start only at certain positions.
  • the start position may be fixed or may be dependent on side information (and derived by the decoder), so the signaling of the start position may be skipped. Instead, one or more the techniques described above may be applied.
  • the implicit start position derivation and the implicit run derivation may also be combined using the same method as described above.
  • a flag or other syntax element may indicate whether the pixel is obtained from the palette or from the previous lines, and then an index indicates the entry in the palette or the row, and finally the 'run.
  • a video coding device may be configured to encode and decode video data using one or more palette coding modes, wherein the palette coding modes do not include a palette sharing mode.
  • a flag such as palette_share_flag
  • the block of video data from which to obtain the shared palette may be based on predetermined rules (e.g., use the palette of the block to the left or above the current block) or may be otherwise indicated in the encoded video bitstream.
  • palette_share_flag[x0][y0] 1 specifies that the palette for the current coding unit is derived by copying the first PreviousPaletteSize entries from the predictor palette.
  • PreviousPaletteSize is derived as specified in subclause 8.4.5.2.8.
  • palette_share_flag [x0][y0] 0 specifies the palette for the current coding unit is specified as a combination of palette entries from previous coding units and new palette entries which are explicitly signaled.”
  • the palette_share_flag indicates that the current block may reuse the last coded palette from the previously coded block.
  • This method is also known as palette sharing.
  • this flag together with the palette sharing method it represents, is not effective in improving coding efficiency, while also introducing additional parsing and decoding complexity.
  • some redundancies are identified in the signaling process for a syntax element that indicates a run type, such as palette_run_type_flag.
  • a syntax element that indicates a run type such as palette_run_type_flag.
  • the current pixel when the current pixel is the first pixel in a line in a scanning order, and a pixel neighboring the current pixel and above the current pixel is available, the current pixel cannot be in "copy above” mode.
  • the term “above pixel is available” means the above neighbor is within the current block for horizontal scanning or the left neighbor is within the block for vertical scanning order if the "copy from outside” methods are not enabled. When the "copy from outside” methods are enabled, the “above pixel” may always be available for each pixel within the block. Example “copy from outside” methods are described in Y.-C. Sun, J.
  • the current pixel's index equals the index of the current pixel's above neighbor. Contrarily, due to the rule that "copy above” mode cannot be immediately followed by another "copy above” mode, the above neighbor must be the end of a 'copy index' run. Therefore, the above neighbor's "copy index” run can be lengthened by at least 1 by adding the current pixel into the "copy index” run instead of making the current pixel the first pixel of a "copy above” run. Thus it is possible to normatively disable "copy above” mode, if the current pixel is the first pixel in a line in a scanning order. This results in bit savings since, for such a pixel, the run type may be inferred to be "copy index", thus eliminating the need to signal such an index.
  • palette_num_signalled_entries indicates the number of entries in the current palette (e.g., a palette to be used to code the current block of video data) that are explicitly signaled.
  • the number of samples that are explicitly signaled may be determined by the difference between the number of entries in the palette subtracted from the number of entries in the palette that are predicted from the palette of another block of video data (including any palette entries that indicate the use of an escape sample).
  • the palette_num_signalled_entries syntax element may be named the num_signalled_palette_entries syntax element.
  • the codeword used to code the value of the palette_num_signalled_entries syntax element may be undesirably long, which may result in codewords of length greater than 32. For example, in HEVC1, all codewords are of length 32 or less. The same situation may also occur when coding the value of the palette_predictor_run syntax element.
  • the palette_predictor_run syntax element specifies the number of zeros that precede a non-zero entry in the array predictor_palette_entry_reuse_flag.
  • the predictor_palette_entry_reuse_flag indicates whether or not a particular palette entry from one or more previously-used palettes is reused for the current palette.
  • the value of palette_predictor_run may range from 0 to the maximum palette predictor size, inclusive.
  • video encoder 20 and video decoder 30 be configured to perform a palette-based coding mode without palette-sharing techniques. More specifically, video encoder 20 and video decoder 30 may be configured to perform palette-based coding without using the palette_share_flag[x0][y0] syntax element, as indicated below:
  • video encoder 20 and video decoder 30 may be configured to code a palette for use with one more blocks of video data using other techniques, such as palette prediction techniques described above.
  • video encoder 20 and/ video decoder 30 may be configured to perform palette prediction using the following techniques.
  • FIG. 4 is a block diagram showing palette-based encoding unit 122 of video encoder 20 in more detail.
  • Palette-based encoding unit 122 may be configured to perform one or more of the example techniques of this disclosure for palette-based video coding.
  • palette-based encoding unit 122 may be configured to encode a block of video data (e.g., a CU or PU) with a palette-based encoding mode.
  • a palette may include entries numbered by an index and representing color component values (for example, RGB, YUV etc.) or intensities which may be used to indicate pixel values.
  • Palette generation unit 203 may be configured to receive pixel values 212 for a current block of video data and generate a palette of color values for the current block of video data. Palette generation unit 203 may use any techniques for generating a palette for a current block of video data, including the histogram-based techniques discussed above.
  • Palette generation unit 203 may be configured to generate a palette of any size.
  • palette generation unit 203 may be configured to generate 32 palette entries, where each palette entry includes pixel values for the Y, Cr, and Cb components of a pixel.
  • each palette entry specifies the values for all color components of a sample (pixel).
  • the concepts described in this document are applicable to using a separate palette for each color component.
  • map unit 204 may generate a map for the current block of video data that indicates whether or not a particular pixel in the current block of video data may be represented by an entry in the palette generated by palette generation unit 203.
  • Map unit 204 may produce a map 214 that includes syntax elements that indicate how each pixel uses (or does not use) entries from the palette.
  • escape pixels are not signaled with a separate syntax element, but rather, may be indicated with a predetermined reserved index in a palette. If the value for a pixel in the current block of video data is not found in the palette, map unit 204 may indicate the use of an escape pixel with the reserved index in the palette and explicitly transmit a pixel value for that particular pixel.
  • map unit 204 may predict the explicit pixel value from one of the entries found in the palette. In some other examples, map unit 204 may quantize the pixel and transmit the quantized values.
  • palette-based encoding unit 122 may also be configured to signal the palette that is to be used for a current block of video data.
  • palette-based encoding unit 122 may be configured to employ palette prediction techniques to reduce the amount of data that is signaled to indicate the values of a palette for a particular block of video data.
  • a palette may include entries that are copied from a predictor palette.
  • a predictor palette may include palette entries from previously-coded blocks that use palette mode or from other reconstructed samples.
  • palette-based encoding unit 122 may include a predictor palette buffer 210.
  • Predictor palette buffer 210 may be configured to store a number of previously-used palette entries from previously-encoded blocks.
  • predictor palette buffer 210 may be configured as a first-in, first-out (FIFO) buffer of a predetermined size. Predictor palette buffer 210 may be of any size. In one example, predictor palette buffer 210 includes up to 64 previously-used palette entries.
  • palette-based encoding unit 122 may be configured to prune the entries in predictor palette buffer 210 such that all palette entries in predictor palette buffer 210 are unique. That is, for each new palette entry to be added to predictor palette buffer 210, palette-based encoding unit 122 may be configured to first check that there are no other identical entries already stored in predictor palette buffer 210. If there are no identical entries, the new palette entry is added to predictor palette buffer 210. If the new entry is a duplicate of an existing entry, the new palette entry is added to predictor palette buffer 210 and the duplicated entries are removed from predictor palette buffer 210.
  • a binary flag e.g., predictor_palette_entry_reuse_flag
  • palette-based encoding unit 122 may be configured to explicitly signal some values for the current palette that cannot be copied from entries in the predictor palette buffer 210. The number of new entries may be signaled as well.
  • video encoder 20 and/or video decoder 30 may be configured to signal the number of explicitly signaled palette entries using the palette_num_signalled_entries syntax element.
  • video encoder 20 and video decoder 30 may be configured to code, among other syntax elements, a syntax element that indicates the number of palette entries that are explicitly signaled for a current palette to be used to code the current block of video data (e.g., palette_num_signalled_entries).
  • a syntax element that indicates the number of palette entries that are explicitly signaled for a current palette to be used to code the current block of video data (e.g., palette_num_signalled_entries).
  • palette-based encoding unit 122 may be configured to encode the first bin of a syntax element that indicates a number of entries in a current palette that are explicitly signaled, such as the palette_num_signalled_entries syntax element, using a CABAC context. Palette-based encoding unit 122 may code other bins of the palette_num_signalled_entries using other encoding techniques. In another example of the disclosure, palette-based encoding unit 122 may be configured to use more than one context to code the first bin of the palette_num_signalled_entries syntax element. In one example, palette-based encoding unit 122 may be configured to determine the contexts based on a block size of the current video block being coded and/or based on the value of other syntax elements.
  • palette-based encoding unit 122 may be configured to determine a first bin of a first syntax element that indicates a number of entries in a current palette that are explicitly signaled. Video encoder 20 may be further configured to encode a bitstream that includes the first syntax element. The bitstream also may not include a second syntax element that indicates a palette sharing mode. In some examples, palette-based encoding unit 122 may be configured to encode the first bin of the first syntax element using a context-adaptive binary arithmetic coding. In other examples, palette-based encoding unit 122 may be configured to encode the first bin of the first syntax element using one or more contexts. In some examples of using one or more contexts, the one or more contexts may be based on at least one of a predicted number of palate coding entries or a block size.
  • a syntax element that specifies the maximum allowed palette size such as palette_max_size
  • a syntax element that specifies the maximum predictor palette size such as palette_max_predictor_size
  • a threshold may be predetermined and stored in a memory (e.g., video data memory 98 in FIG.
  • palette_max_size the value may be any value from 0 to T1, inclusive, where T1 is the threshold.
  • palette-based encoding unit 122 may be configured to infer the value of palette_max_size to be 0.
  • palette_max_predictor_size the value may be any value from 0 to T2, inclusive, where T2 is the threshold.
  • palette-based encoding unit 122 may be configured to infer the value of palette_max_predictor_size to be 0.
  • T1 is equal to 4096 and T2 is equal to 8192. In another example, T1 is equal to 4095 and T2 is equal to 4095. In yet another example, T1 is equal to 4095 and T2 is equal to 8191.
  • palette-based encoding unit 122 may be configured to code the value of the palette_num_signalled_entries syntax element using one more coding techniques from the Golomb code family (e.g. Golomb-Rice code, Exponential Golomb code, Truncated Rice code, Unary code, etc.).
  • Golomb code family e.g. Golomb-Rice code, Exponential Golomb code, Truncated Rice code, Unary code, etc.
  • palette-based encoding unit 122 is configured to encode the value of the palette_num_signalled_entries syntax element using an exponential Golomb code of order 0.
  • palette-based encoding unit 122 is configured to encode the value of the palette_num_signalled_entries syntax element using a concatenation of a Truncated Rice (TR) code and an exponential Golomb code such as the one used in coefficient coding to code coeff_abs_level_remaining syntax element in HEVC1.
  • TR Truncated Rice
  • a concatenation of a TR code and an exponential Golomb code for Golomb Rice parameter of 0 is shown below: Symbol binarization 0 0 1 10 2 110 3 1110 [4, 5] 11110x [6, 9] 111110xx [10, 17] 1111110xxx ...
  • x can take a value of 0 or 1.
  • the table below shows an example of a concatenated binarization used in the coding of paletteRun syntax element. This is a concatenation of a truncated Rice and truncated exponential Golomb code of order 0 for maximum run value of 7.
  • x can take a value of 0 or 1.
  • Using one or more Golomb codes (e.g., such as an exponential Golomb code or a concatenation of TR code and an exponential Golomb code) to code the palette_num_signalled_entries syntax element provides a benefit compared to previous techniques for coding the value of the palette_num_signalled_entries syntax element.
  • Previous techniques for coding the value of the palette_num_signalled_entries syntax element used a unary code. Use of a unary code resulted in the coded length of the palette num_signalled _entries syntax element being larger than 32 bits in some circumstances.
  • the techniques of this disclosure allow palette-based encoding unit 122 to encode the value of the palette num_signalled _entries syntax element in a matter that keeps the coded length at or below some predetermined number of bits (e.g., 32 bits).
  • palette-based encoding unit 122 may be configured to code the value of the palette_num_signalled_entries syntax element using truncated version of a Golomb code family (e.g., truncated Golomb Rice code, truncated Exponential Golomb code, truncated Truncated Rice code, truncated Unary code, etc.).
  • palette-based encoding unit 122 may be configured to code the value of the palette num_signalled _entries syntax element using the same code used to code the paletteRun syntax element.
  • palette-based encoding unit 122 may be configured to code the value of the palette_num_signalled_entries syntax element using the method used to code coeff_abs_level_remaining syntax element in coefficient coding (e.g., concatenation of truncated Rice (TR) and exponential Golomb code).
  • the TR parameter is preferred to be 0.
  • the particular truncated code is chosen such that the encoded length of the palette num_signalled _entries syntax element is kept at or below 32 bits.
  • palette-based encoding unit 122 may be configured to limit the possible value of the palette_num_signalled_entries syntax element by the number of pixels in the currently coded block.
  • palette-based encoding unit 122 may be configured to limit the possible value of the palette_num_signalled_entries by the number of pixels in the largest possible block of a particular picture (e.g., the large block size defined by a particular video coding standard).
  • palette-based encoding unit 122 may be configured to bypass signaling a syntax element that indicates a run type, such as palette_run_type_flag, if the current pixel is the first pixel in the line in scanning order and the pixel neighboring the current pixel above the current pixel is available.
  • palette-based encoding unit 122 may be configured to determine that a current pixel is a first pixel in a line in a scanning order. Palette-based encoding unit 122 may further determine that a neighboring pixel situated above the current pixel is available.
  • palette-based encoding unit 122 may be further configured to bypass encoding a first syntax element in a bitstream, wherein the first syntax element indicates a run type and encode a remainder of the bitstream.
  • palette-based encoding unit 122 may be configured to signal palette entry values in the encoded video bitstream (e.g., using explicit signaling or another prediction technique).
  • video encoder 20 may be configured to encode or generally encode the binary predictor vector b in order to reduce the amount of data needed to signal a palette in the encoded video bitstream.
  • binary prediction vector compression unit 209 may be configured to generate and signal encoded binary prediction vector 215.
  • the binary prediction vector compression techniques of this disclosure may be implemented in other structures of video encoder 20, including entropy encoding unit 118 in FIG. 2 .
  • binary prediction vector compression unit 209 may be configured to encode the binary prediction vector using a run-length based encoding techniques.
  • binary prediction vector compression unit 209 may be configured to encode the binary prediction vector by signaling the number of consecutive '0s' between 'Is' in the binary prediction vector using an Exponential-Golomb code.
  • b [110010001000]. In this example, as shown in FIG.
  • the binary prediction vector (i.e., b ) can be expressed as: ' zero consecutive 0s'-'1'-' zero consecutive 0s'-'1'-' two consecutive 0s'-'1'-' three consecutive 0s'-'1'- and ' four consecutive 0s'. Because it is known that b i ⁇ ⁇ 0,1 ⁇ , except for the last 'consecutive 0' group, each 'consecutive 0' group must be followed by a '1'.
  • binary prediction vector compression unit 209 may use zero-based run-length coding techniques to represent the binary prediction vector b as ' zero consecutive 0'-' zero consecutive 0'-' two consecutive 0'-' three consecutive 0'-' four consecutive 0', which can be expressed as the run-length sequence '0-0-2-3-4'.
  • a Golomb-Rice code In accordance with one or more examples of this disclosure related to run-length based signaling, to code the run-length sequence, a Golomb-Rice code, Exponential-Golomb code of any order, Truncated Exponential-Golomb code, Truncated-Rice code or any other binarizations, including truncated binarizations, may be used.
  • binary prediction vector compression unit 209 uses a 0-th order Exponential-Golomb code as the run-length coding technique.
  • the maxsymbol can be the maximum possible value of the run depending on the position of '1' in the binary vector and the binary vector size, since, upon moving to the end of the binary vector, the maximum possible run value is reduced from the vector size to 0 depending on the position within the vector.
  • the max symbol can be the binary vector length or the binary vector length minus the position of the ' 1' from which the run is being counted. In, other words, it is the remaining length measured from the end of the binary vector.
  • the run-length sequence '0-0-2-3-4' can be coded with the truncated binarization 0[13]-0[12]-2[11]-3[8]-4[4]', where the max symbol is provided in the brackets.
  • binarization may be dependent on the position or index of the element (0 or 1) in the binary vector. As a particular example, if the position is smaller than a certain threshold, one type of binarization is used; otherwise, another type of binarization is applied.
  • the binarization type can be different binarization codes, or the same code family but with different order, such as Exponential-Golomb code.
  • the threshold may be the palette length from the previous block or previous palette coded block. In another example, the threshold can be fixed to some default value or signaled per block, slice, picture or elsewhere. It is to be recognized that a corresponding technique may optionally be used to define a CABAC context to code the run values.
  • palette-based encoding unit 122 (See FIG. 2 ) may be configured to stop run-length signaling when the number of signaled '1' elements (i.e., the number of palette entries from predictor palette buffer 210 indicated as being reused for the current palette 220) reaches a maximum possible number. In some examples, the maximum possible number is the maximum possible palette size.
  • binary prediction vector compression unit 209 is configured to add 1 to the run-length. If the actual run-length is less than L , binary prediction vector compression unit 209 is configured to signal the run-length as is.
  • Binary prediction vector compression unit 209 may signal the end position run-length with the reserved run-length L .
  • FIG. 7 is a block diagram showing an example of palette-based decoding unit 165 of video decoder 30.
  • Palette-based decoding unit 165 may be configured to perform in a reciprocal manner to palette-based encoding unit 122 of FIG. 4 .
  • Palette-based decoding unit 165 may be configured to receive a map 312 that indicates, for each pixel in a current block, whether or not entries for a palette will be used for the pixels in the current block.
  • map 312 may further indicate what palette entries are to be used for a given pixel.
  • Map unit 302 may decode the current block of video data using the map 312 and a palette generated by palette generation unit 304 to produce decoded video data 314.
  • palette-based decoding unit 165 may also receive an encoded binary prediction vector 316.
  • binary prediction vector 316 may be encoded using a run-length coding technique that encodes a run-length sequence indicating a run of zero values in the binary prediction vector.
  • Binary prediction vector decompression unit 306 may be configured to decode the encoded binary prediction vector 316 using any combination of the run-length coding techniques described above with reference to FIGS. 4-6 .
  • palette generation unit 304 may generate a palette for the current block of video data based on the binary prediction vector and previously-used palette entries stored in predictor palette buffer 310.
  • Palette-based decoding unit 165 may be configured to store previously-used palette entries in predictor palette buffer 310 in the same manner that palette-based encoding unit 122 (see FIG. 2 ) stored previously-used palette entries in predictor palette buffer 210.
  • palette-based decoding unit 165 may be configured to decode the first bin of a syntax element that indicates a number of entries in a current palette that are explicitly signaled, such as the palette_num_signalled_entries syntax element, using a CABAC context. Palette-based decoding unit 165 may decode other bins of the palette_num_signalled _entries using other decoding techniques. In another example of the disclosure, palette-based decoding unit 165 may be configured to use more than one context to decode the first bin of the palette_num_signalled_entries syntax element. In one example, palette-based decoding unit 165 may be configured to determine the contexts based on a block size of the current video block being decoded and/or based on the value of other syntax elements.
  • palette-based decoding unit 165 may be configured to determine a first bin of a first syntax element that indicates a number of entries in a current palette that are explicitly signaled. Video decoder 30 may be further configured to decode a bitstream that includes the first syntax element. The bitstream also may not include a second syntax element that indicates a palette sharing mode.
  • palette-based decoding unit 165 may be configured to decode the first bin of the first syntax element co using a context-adaptive binary arithmetic coding.
  • palette-based decoding unit 165 may be configured to decode the first bin of the first syntax element using one or more contexts. In some examples of using one or more contexts, the one or more contexts may be based on at least one of a predicted number of palate coding entries or a block size.
  • palette-based decoding unit 165 may be configured to infer the value of palette_max_size to be 0. Further, for palette_max_predictor_size, the value may be any value from 0 to T2, inclusive, where T2 is the threshold. When not present, palette-based decoding unit 165 may be configured to infer the value of palette_max_predictor-size to be 0.
  • T1 is equal to 4096 and T2 is equal to 8192. In another example, T1 is equal to 4095 and T2 is equal to 4095. In yet another example, T1 is equal to 4095 and T2 is equal to 8191.
  • palette-based decoding unit 165 may be configured to decode the value of the palette_num_signalled_entries syntax element using truncated version of a Golomb code family (e.g., truncated Golomb Rice code, truncated Exponential Golomb code, truncated Truncated Rice code, truncated Unary code, etc.).
  • palette-based decoding unit 165 may be configured to decode the value of the palette_num_signalled_entries syntax element using the same code used to code the paletteRun syntax element.
  • palette-based decoding unit 165 may be configured to decode the value of the palette num_signalled_entries syntax element using the method of decoding coeff_abs_level_remaining syntax element in coefficient decoding (e.g., concatenation of Truncated Rice (TR) and exponential Golomb code).
  • the TR parameter is preferred to be 0.
  • palette-based decoding unit 165 may be configured to limit the possible value of the palette_num_signalled_entries syntax element by the number of pixels in the currently coded block.
  • palette-based decoding unit 165 may be configured to limit the possible value of the palette_num_signalled_entries by the number of pixels in the largest possible block of a particular picture (e.g., the large block size defined by a particular video coding standard).
  • palette-based decoding unit 165 may be configured to infer value of a syntax element that indicates a run type, such as palette_run_type_flag, if the current pixel is the first pixel in the line in scanning order and the pixel neighboring the current pixel above the current pixel is available.
  • palette-based decoding unit 165 may be configured to determine that a current pixel is a first pixel in a line in a scanning order. Palette-based decoding unit 165 may further determine that a neighboring pixel situated above the current pixel is available.
  • palette-based decoding unit 165 may be further configured to infer the value of the first syntax element in a bitstream, wherein the first syntax element indicates a run type and encode a remainder of the bitstream.
  • the first syntax element is a palette_num_signalled_entries syntax element.
  • the plurality of syntax elements includes the palette values indicated as being explicitly signaled by the first syntax element.
  • the predetermined maximum number of bits is 32, and the one or more Golomb codes is an exponential Golomb code of order 0. In another example of the disclosure, the predetermined maximum number of bits is 32, and the one or more Golomb codes is a concatenation of a truncated Rice code and an exponential Golomb code.
  • a maximum value of the first syntax element is defined relative to a second syntax element that indicates a maximum size of the palette, and a third syntax element that indicates a maximum size of a palette predictor.
  • video encoder 20 may be further configured to define the second syntax element to be less than or equal to a number of pixels in a largest possible block in the encoded video bitstream, and define the third syntax element to be less than or equal to K * a value of the second syntax element, where K is a positive constant. In one example, K is 2.
  • FIG. 9 is a flowchart illustrating an example video decoding method according to the techniques of the disclosure.
  • the techniques of FIG. 9 may be implemented by one or more hardware structures of video decoder 30, including palette-based decoding unit 165 and/or entropy decoding unit 150 (see FIG. 3 ).
  • Video decoder 30 may be further configured to decode the plurality of syntax elements, including decoding the first syntax element using the one or more Golomb codes (904), reconstruct the palette based on the decoded plurality of syntax elements (906), and decode the block of video data using the reconstructed palette (908). Video decoder 30 may be further configured to display the decoded block of video data.
  • such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.
  • any connection is properly termed a computer-readable medium.
  • a computer-readable medium For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium.
  • DSL digital subscriber line
  • Disk and disc includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.
  • processors such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry.
  • DSPs digital signal processors
  • ASICs application specific integrated circuits
  • FPGAs field programmable gate arrays
  • processors may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein.
  • the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.
  • the techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set).
  • IC integrated circuit
  • a set of ICs e.g., a chip set.
  • Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

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